1. Technical Field of the Invention
The invention relates generally to a method for measuring the thickness of print products, and more particularly, to a method for measuring the thickness of print products flowing through a measuring device in spaced intervals.
2. Related Art
Conveying systems that operate on a timed cycle commonly include a rotating drum having grippers that grip print products to be separated, and transfer the print products to one or more conveying belts. The thickness of the print products can be measured on the rotating drum or on the downstream conveying device (e.g. between belts). Known systems detect the product thickness, for example, by mechanical means, for example, by scanning the thickness of the product and measuring the deflection thereof. Swiss Patent No. 671 754 discloses one known device for measuring the thickness of print products on a rotating drum with grippers.
Known measuring systems have various disadvantages. For example, taking the measurement on a rotating drum having grippers only makes sense if the withdrawing device also utilizes grippers. Also, scanning with rollers can be mechanically involved, in particular, in cases where the cycle rate is high, thicknesses vary greatly, or markings must be prevented.
Some non-contacting systems for measuring the thickness of print products are also known. Known non-contacting systems typically measure the degree of light absorption and/or ultrasound absorption by the print product and use the obtained value as a measure for the thickness of the print product. These methods, however, can only be used with extremely thin products.
Other known arrangements measure the thickness of paper during winding and/or unwinding of paper rolls, or measure the thickness of labels on a backing strip by measuring capacitance. Features of these measuring arrangements are based on bridge circuits where the measured capacitance is electronically compared to a reference capacitance.
This type of measurement uses an analog signal, the magnitude of which reflects the measured capacitance value. Usually, the reference capacity must be equalized manually.
Solutions of this type have the disadvantage that in most cases individual equalization of the device is required. Another disadvantage is that the analog signal which represents the capacitance is subject to interference, so that involved configurations are often necessary.
Therefore, there remains a need in the art for a measuring device for print products flowing through the measuring device in spaced intervals, that overcomes the shortcomings of conventional solutions.